Imaging apparatus using liquid toner development systems are well known in the art. A typical liquid toner development system includes a developer surface which engages a selectively discharged photoreceptor surface at a development region. The liquid toner is applied to either the developer surface or the photoreceptor surface, ahead of the development region, or directly to the development region. Thus, subsequent engagement between the developer surface and the photoreceptor surface results in development of a layer of liquid toner on at least a portion of the photoreceptor surface.
There are various devices known in the art for supplying liquid toner in the development systems described above. According to one known method, the liquid toner is applied to the developer surface by a sponge which collects the toner from a toner reservoir. According to another known method, the toner is pumped from the reservoir and sprayed by a set of sprayers which are juxtaposed with the developer or photoreceptor surface along the width thereof. For color development, a plurality of sets of sprayers may be used, one for each color toner, or the different color toners may be sequentially pumped to the same set of sprayers.
Although the sprayer method is preferred because it allows a higher imaging speed, this method still has drawbacks. Since a number of sprayers are used to cover the entire width of the photoreceptor surface, the resultant toner layer is not completely homogeneous because regions of the photoreceptor directly across from the sprayers are generally supplied with more toner than other regions of the photoreceptor. This may result in the appearance of streaks, on the final image, which are particularly noticeable in high resolution printing. The apparentness of such streaks may be reduced by using a higher density of sprayers, for example using a staggered arrangement of sprayers, or by distributing the liquid toner relatively evenly on the developer roller before contact with the photoreceptor surface. However, such methods are not always completely effective.
Japanese Patent Application 5-46029 describes a development system for electrostatic imaging apparatus which uses a toner applicator having an elongated, slit-shaped, nozzle, juxtaposed with the development region between the photoreceptor and developer surfaces. The slit applicator provides a generally continuous body of toner to the development region. The specified width of the slit is between 10-3000 .mu.m. For development of color images, a plurality of such slit applicators, each applicator being supplied with a different color toner, are sequentially brought into juxtaposition with the photoreceptor surface. To avoid dripping of toner from the applicator, Patent Application 5-46029 suggests using an outlet control valve, at the slit outlet of each applicator, to bar the outlet of toner between imaging cycles.
It is believed that use of existing slit applicators, such as these suggested in Patent 5-46029, is not practical due to a number of problems. For example, the use of exit valves for controlling the flow of toner through the slit applicators, to avoid dripping from the applicators, is difficult to implement. Additionally, in color imaging systems, the need to physically switch between the different color applicators may consume considerable space and time and may be complicated to implement.